(1) Field of the Invention
The present invention relates to a sheet post-processing device mounted in an image forming apparatus, and also to an image formation system including the image forming apparatus and the sheet post-processing device.
(2) Related Art
Among image forming apparatuses such as copiers, there is a so-called in-body ejection type. In this type of image forming apparatus, an image forming unit is provided under an image reading unit with a space therebetween. After an image is formed on a recording sheet or the like by the image forming unit, the recording sheet is housed into an ejection tray provided in the space. With the in-body ejection type, the ejection tray does not protrude from a side surface of the image forming apparatus, and the space occupied by the image forming apparatus can be reduced.
Japanese Patent Application Publication No. 2002-128364 discloses an in-body ejection type image forming apparatus in which a sheet post-processing device is mounted. The sheet post-processing device is provided in a space (in-body space) between an image reading unit and an image forming unit, and performs post-processing, such as stapling, on a sheet ejected from the image forming unit.
The sheet post-processing device includes a processing tray and a stack tray. The processing tray temporarily houses a stack of sheets after images are formed thereon, so that post-processing is performed on the stack of sheets. The stack tray houses the stack of sheets transferred from the processing tray after the post-processing. When seen from the front side of the image forming apparatus, the processing tray and the stack tray are aligned side by side in the left-right direction, where the stack tray is closer to the right side of the image forming apparatus than the processing tray.
The aforementioned publication includes a plan view in which the stack of sheets housed in the stack tray is easily seen, and discloses that the user can easily take the stack of sheets after post-processing.
However, if the processing tray and the stack tray are aligned side by side in the left-right direction within the in-body space as disclosed in the above publication, the size of the sheet post-processing device in the left-right direction becomes large. As a result, the in-body space of the image forming apparatus also needs to be increased in the left-right direction according to the size of the sheet post-processing device.